A person breathes in and out every 3 seconds. The volume of air in his lungs (as shown in the figure) varies between a minimum of 1.0 liter and a maximum of 5.0 liters. Let t = 0 be the time this person just starts to breathe OUT (MAXIMUM volume of air in lung).
(1) Based on the graph, find period, amplitude of this periodic function.
(2) find a formula of this function.
(3) At t = 20, what is the volume of air in this person's lungs?
You need to provide work in steps which shows how you derive the answers.